In a Malaysian zoo, a siamang has attacked and severely injured a three-year-old boy.
The siamang is the largest of the gibbons or "lesser" apes--as opposed to the better known "great" apes, including the chimpanzees, orangutans, and gorillas. This article lists the attacker at 38 kilos (84 pounds), which is probably a typo; the average for this species is under 30 pounds, though they may stand four feet tall or so as they waddle on the ground. They'd prefer to swing by their arms.
The news report (linked below) gives no information on the reason for the attack, though all primates are potentially dangerous and can become aggressive for no obvious reason.
The most startling characteristic of the siamang, aside from biting zoo visitors, is its habit of inflating its neck to the size of a pumpkin and bellowing like a game show contestant imitating a pig. This sound can be heard by gibbons in the next neighborhood.